The keratin fibers are filiform structures comprised of keratin cells produced by the hair follicle, which has color, variable structural and morphological characteristics according to their location and age, which can include hair and body hair in general, eyebrows, eyelashes, moustache, beard and other human being or animal hair, or synthetic substrates.
Human hair, for instance, has a complex structure that consists of three different morphological components, and keratin is the primary element, which corresponds to at least 65% of the keratin fiber. The central portion of the fiber is known as medulla. It is surrounded by the cortex, which is a layer composed of keratin cells that provide mechanic force to the entire fiber. The outermost layer is the cuticle, a thin layer of overlaid keratin scales, which serves as a protective barrier.
The natural color of these fibers derives from the pigment particles that are produced in the melanocytes and transferred to the cortex and medulla cells. The natural variations, oxidation degree, amount and distribution of these natural pigments along the fiber cause the various hues. The natural color of the human hair, for example, is mainly the result of two types of pigments: eumelanin (black) and pheomelanin (red).
Due to the intrinsic human desire to improve his/her appearance, a number of products designed to change the natural color of the keratin fibers are available in the market. The most common and utilized are the semi-permanent and permanent fiber coloring products.
The semi-permanent or deposition fiber coloring products, also known as tonalizers, include products that are capable of changing the natural color of the keratin fibers to some extent, being gradually washed away at every wash. These products must be ready to use and easy to apply and include low molecular weight and high keratin affinity coloring agents in their formula, for instance, those of the nitro-family, as well as the nitroanilines, nitrophenylenediamines and nitroaminophenol derivatives, which penetrate into the cuticle and partially into the fiber cortex, which results in an average resistance from 5 to 12 washes.
The choice between the coloring agents is a big barrier against the formulation of this type of product, because the affinity of these agents along the different portions of the fiber length is not homogeneous, i.e., certain compounds have affinity for these more damaged regions (tip-ends) while others for less damaged regions (root).
Permanent fiber coloring products, also called oxidant fiber coloring products, are the only ones that can provide long lasting color, with the options for many tonalities and more extensive cover to the fibers.
In the permanent tinting process, the original color of the fiber shall be made unnatural so as to form afterwards a new color by means of oxidative condensation. In order for permanent color fixation to occur, the reaction that forms the coloring agent must occur in contact with the keratin fiber. For this purpose, the permanent fiber color products are divided in a first composition, which contains the coupling basis (coloring agents) and an alkaline agent and a second composition containing the oxidant agent, usually hydrogen peroxide.
The coupling basis consists of dye primary intermediates, which are modified during the reaction of oxidation, developing the colors. This category includes the aromatic diamines, aminophenols and diaminophenols. These intermediates are the key to create basic hues as well as to cover dispigmented fibers.
The couplers or modifiers are responsible for the colors themselves. Separately they only produce weak colors, but when reacted with the bases, in presence of an oxidant agent, in alkaline medium, they modify the colors of the bases, generating new colors to the keratin fibers. The most employed modifiers are m-diamine, m-aminophenol and polyphenols. Some heterocyclic derivatives are used as couplers, in order to increase the durability of the fiber coloring products and avoid discoloration after a number of washes, for example, 6-hidroxindol and 2-amino-3-hidroxipiridine.
When the two phases are mixed, an oxi-reduction occurs and leads to the formation of the color itself. Simultaneously, part of the hydrogen peroxide will dissolve the natural pigment of the fiber that is being attacked by the alkaline agent, usually ammonia or monoethanolamine. The solubilization of the natural pigment will cause this latter to be replaced by the color agent that is forming during the oxi-reduction reaction, generating the new color.
Various external factors can provoke the degradation of the colors obtained by semi-permanent or permanent fiber coloring products, for example, light, heat, pollution, water hardness, UV radiation, etc. In the case of permanent fiber coloring products, these factors can be worsened if there is excess of couplers, which might generate excess of undesirable byproducts. Other influent factor is the reaction speed, for the oxidation process must be controlled so as to take place inside the cuticle of the keratin fiber in order to, in a certain period of time, complete the reaction. When the reaction occurs in less time than required, the formed coloring agent will be located in the external region of the keratin fiber and will be washed away and when it is superior to the required, the reaction will not be completed at the process end. In this sense, an important aspect is the permeation of the coloring agents and their spread along the keratin fibers.
The appropriate carrier for these products can include solution, liquid, emulsion, pseudo-emulsion, oil that converts into gel, gel, shampoo or powder, being barrier, in some cases, the complete dispersion of the coloring agents in these mediums.
To solve the above-mentioned problems, the fiber coloring compositions usually count only on the coloring agent characteristics. Some compositions had cationic and/or amphoteric compounds added to them, which are quaternary or polyquaternary, etc., as exemplified in the patents FR 2402446, FR2428438, FR2687570 and U.S. Pat. No. 3,986,825, which allow more vibrant colors and less tendency to lose color, but they do not interfere with the diffusion of the coloring agents nor swelling of the capillary fiber nor homogeneity of the color.
Thus, it is desired improvements regarding the manufacturing process of semi-permanent and permanent coloring products for keratin fibers and concerning the attributes and quality of these products.